Python

Over on the Memonic blog I blogged about why and how we work with Python at Memonic. As the original blog is now archived, I later reproduced the article below. Python Fun fact: Memonic is written entirely in Python. Why did we choose this particular programming language? After all - aren’t all the serious developers on Java and the cool ones on Ruby? When we thought about the programming language to use, we already knew how our architecture was going to look, namely that we’d have a frontend and lots of small backend web services. That’s a setup we had previously implemented successfully at local.ch. But at local.ch we had the frontend in PHP and the backend in Java. At Memonic we wanted everything to run on one language so every developer could feasibly work on the whole stack. This threw out PHP which isn’t so great for daemons and services (but I still like it for frontend work, especially with Okapi). We then had Ruby, Java and Python in the race. Without going into detail about why the other two languages suck ;-) Python won us over because of it’s maturity and the very wide selection of frameworks and libraries. ...

For returning complex values from a method you have a few popular choices: Return a tuple with positional values. Those are very easy to unpack in Python and quite attractive because of that. Return a dictionary with the values. This can lead to slightly verbose accessing of the individual values. Return an object of some class you define. This required the definition of a class which can be too verbose for just a simple return value. Since Python 2.6 you have one additional tool: collections.namedtuple. They give you a very lightweight class but it’s a one-liner to define them. ...

nose is my Python testing tool of choice. You can use it to very easily create test suites. While it does support the unittest module which is included with Python, it also allows for a much simple style using just methods and asserts. Put the following code into a file called test_basic.py: <notextile>def test_addition(): print 2 + 2 assert 2 + 2 == 4 def test_addition_wrong(): print 2 + 3 assert 2 + 3 == 6</notextile> Then just run nosetests in the directory where you stored this file. You’ll get an output indicating, that there is a test failure. ...

Tomorrow (March 31) we’ll hold the second swiss.py user group event. We’ll meet at the main ETH building at 19:30. If all goes well, Florian Bösch will talk about OpenGL development using Python. He’s currently not feeling that well, so the topic might change on the day itself. Get more details on the official swiss.py web site.

Python’s with statement can be a very elegant alternative to long try/except/finally clauses. It offers a standard protocol that classes can implement to properly clean up state. The best example for it’s value is file reading. A good implementation would have to look like this traditionally: f = open('/tmp/myfile', 'r') try: content = f.read() finally: f.close() The with statement shortens this to the following code: with open('/tmp/myfile', 'r') as f: content = f.read() Behind the scenes it wraps the finally statement around this and makes sure that the file gets closed upon leaving the with block. ...

As most programmers, I’ve been trained with the getter/setter idiom. It allows a programmer in any object-oriented programming language to create a class interface which makes sure that only valid data is written. An example of a class with getter/setter in Python: class Person1(object): def __init__(self): self._age = None def get_age(self): return self._age def set_age(self, age): self._age = age We just wrote two methods - four lines - only to be able to modify and access some data. And we have to do that for every property. This is such a common idiom, that IDEs even have wizards for that. ...

Starting with Python 2.6 there is a new format function to do string formatting. I’ve always been a bit overwhelmed by the official Format String Syntax documentation so I’ll try to present it to you with more examples. Python so far had the ‘%’ operator. It’s been deprecated with Python 2.6 and removed from Python 3. Instead string has a new format method. >>> "This is an %s-style formatting" % "old" 'This is an old-style formatting' >>> "This is a {0}-style formatting".format("new") 'This is an new-style formatting' Formatting options go after a colon, for example the width specifications together with alignment options which are mostly useful for tabular representations. Let’s print the following table as an exercise: ...

With the Pot: String formatting I’m starting a series on my blog: Python on the toilet. I’ll try to write short and dense introductions for Python features or packages. Each introduction should fit on a A4 paper. So if you want to, you could print it out and hang on your toilet doors. I’m not entirely sure yet what I’ll cover, but we’ll see what comes up. If you have topic proposals shoot me a mail. ...

Yesterday evening we had the very first swiss.py. Thanks to Uche Mennel for doing a very interesting presentation about Traits. I was really happy about the number and diversity of people who showed up. The next swiss.py will take place on March 31 with Florian Bösch doing a presentation related to OpenGL programming in Python. Details and location will follow.

I’m pretty programming language agnostic and fluent in a handful of different languages. That means I use the language that gets the job done. But I tend to lean towards dynamic programming languages specifically PHP, Python and Ruby. Last week I had to solve a non-trivial problem for my background: clustering of content. I had to write a program which takes a bunch of search results and clusters them together by content. So similar results would go into the same group. ...